Aeronautical spanner nuts are used to secure power transmission drive flanges to the input and output ends of power transmission drive shafts on helicopter tail rotor drive systems. Each drive flange and the drive shaft are provided with splines to prevent relative movement therebetween, and a spanner nut holds the flange on the drive shaft.
To properly torque a spanner nut on the threaded end of a drive shaft, up to several thousand inch pounds of torque must be applied. Because of the location of the spanner nut within the drive flange, special power transmission tools have been developed to apply the proper torque when attaching the spanner nut, and for applying torque to remove the spanner nut. Referring to FIG. 1, present tools used to attach aeronautical spanner nuts typically include a cylindrical wrench 10 which is concentrically piloted within a torque reactor plate 12. An aperture 13 in the torque reactor plate and the surface of the wrench act as a bearing and hold the wrench in alignment with a spanner nut 15. During installation or removal of the spanner nut, the torque reactor plate 12 is mounted to a drive flange 20 with a plurality of fasteners 23. An aperture 25 is formed in the reactor plate to receive a bar or other tool (not shown) to react the torque applied to the wrench 10, thereby preventing the transmission shaft 27 and flange 20 combination from rotating when torque is applied to the wrench 10, e.g., using a standard torque wrench. Two operators are required during removal or installation of the spanner nut in the field because of the torque involved; one person to operate the torque wrench and one person to apply torque to the reactor plate via the bar.
A problem associated with the present method of installing and removing a spanner nut on the end of a drive shaft is that when torque is applied to the wrench 10, the wrench tends to jump out of and away from the slots of the spanner nut 15. This results in several problems. First, the tangs which project from the wrench for engagement with the spanner nut become rounded or damaged, and the slots in the spanner nut which receive the tangs tend to become rounded. Therefore, the wrench and the spanner nut may become unusable and lead to a great deal of problems in trying to remove the spanner nut 15 without damaging the power transmission shaft 27 and flange 20. Additionally, if the wrench breaks free from the spanner nut when the wrench operator is applying up to several thousand inch pounds of torque, the wrench and/or reactor operator could be injured by the tool or by a fall.